The present invention relates to a water mixer tap of the single-lever type.
As known, mechanical mixers of hot and cold water, commonly known as single-lever mixer taps, wherein a single control element allows to alter both the water mixing temperature and the flow rate of the water dispensed, have been available on the market for some time. Such types of taps have, as a sealing and adjustment element, a ceramic disc whereon act two seats, respectively for hot water and for cold water, which rest on the ceramic disc which can rotate and translate and is provided with one or more ports for the flow of water towards the dispenser.
Such kinds of taps, which are for example described in the U.S. Pat. No. 3,882,897 and in the French Pat. No. 2,208,499, have the advantage of having very small friction surfaces, determined by the region of contact between the seats and the movable disc, with a consequently very smooth operation of the control element and the impossibility of subjecting the control elements and other parts of the tap to excessive and dangerous forces and stresses which depend on the pressures of the water supply.
On the other hand such mixers do not always offer satisfactory possibilities of fine temperature adjustment, since, for manufacture reasons, the seats unavoidably have a circular port and the ports provided on the movable disc, even if variously shaped, are not capable of allowing a variation of the mixing temperature which is proportional to the rotational movement of the operating lever which is performed to vary the mixing temperature.
Other types of known single-lever mixer taps are provided, as sealing element, with the coupling of two ceramic discs having variously shaped water flow ports, mutually mating and precompressed, with the advantage of allowing a fine adjustment of the variation of the mixing temperature, by virtue of the possibility of providing the ports, on both discs, with a shaped configuration, but on the other hand they have a very wide contact surface which creates friction problems upon operation, said discs also being subject to even considerable calcareous deposition, to pressure shocks, that is to the so-called water hammering, to deformations caused by the temperature and by the water hammering, to the friction between the two discs caused by the necessary initial compression for assembly, with the possibility of reaching the mutual jamming of the two discs, in the more severe cases, with the impossibility of operating the control element.